1. Field of the Invention
This invention relates to a cartridge shell for mounting a cartridge used in a phonograph record player and specifically involves the use of a material of construction which provides the shell with improved stiffness and frequency response.
2. Description of the Prior Art
The typical phonograph pickup system employs a tone arm which is pivotally supported on a fulcrum, and carries a cartridge from which there is a depending cantilever which carries a stylus. Generally, the shell in which the phonograph cartridge is mounted is composed of steel or aluminum, but these materials have the disadvantage that their rigidity is not relatively high, and they do not have suitable vibration damping properties.
In order to solve such problems, it has been proposed that a shell be formed by a composite member made of carbonaceous fibers bonded together with a synthetic resin such as phenolic resin, epoxy resin, or the like, as described in U.S. application, Ser. No. 489,073, now U.S. Pat. No. 3,923,309 assigned to the same assignee as the present invention.
In this earlier case, the shell is formed from a large number of fine carbon fibers each having a diameter of about 7 microns and being from 3 to 4 millimeters in length. With a sheet made in such a manner, the reproducing characteristics are improved in comparison with conventional shells. However, since many of the carbon fibers could not be mixtured with resin, for example, a maximum of about 30 percent (in this case, the resin being 70 percent), so that, the equivalent mass is not particularly decreased. Furthermore, the equivalent mass is decreased when a shell is formed by only carbon fibers as described and shown in FIGS. 8 and 9 of said application, Ser. No. 489,073. However, in this case, Ser. No. 489,073, an upper surface of the shell is not shaped well. In other words, there is a great deal of roughness on the upper surface.